This application is a 371 of PCT/JP01/0242 filed Mar. 26, 2001.
The present invention relates to a gas spring and a gas filling method. More particularly, the present invention relates to an improved technique for filling a gas spring with compressed gas.
A gas filling chamber of a conventional gas spring is filled with gas, commonly nitrogen, compressed to a high pressure of about 7-10 Mpa. A gas filling valve, equipped with a nonretum valve, allows the gas filling chamber to be filled with the compressed gas. The gas spring is filled with compressed gas through the gas filling valve during fabrication, and the compressed gas is subsequently replenished through the gas filling valve as the gas pressure decreases.
The applicant has devised and studied the feasibility of applying gas springs to situations in which a drawbar, used to fasten a tool to the main shaft of a machine tool, is driven toward to the tool fastening side. The main shaft of a contemporary machine tool is rotated at a high speed of about 30,000-40,000rpm. When a gas spring is used to fasten the tool to the main shaft of the machine tool, the gas filling valve is mounted at a position away from the center of the main shaft, so the centrifugal force acting on the gas filling valve causes the main shaft to vibrate, resulting in reduced machining accuracy.
In view of this, dispensing with the gas filling valve appears to be the preferred option, however no technique has so far been proposed that would allow the gas filling chamber of a gas spring to be filled with compressed gas without a gas filling valve mounted on the gas spring.
It is an object of the present invention to provide a gas spring which overcomes the foregoing problems.
More specifically, it is an object of the present invention to provide a gas spring, without a gas filling valve.
It is another objection of the present invention to provide a method in which the gas filling chamber of a gas spring can be filled with compressed gas without the use of a gas filling valve.
Briefly stated, the present invention provides a gas spring and a method for filling a gas chamber of a gas spring which does not require the use of a gas filling valve. A gas spring includes a rod member, a cylinder main body, a gas filling chamber, first and second sealing members, a plurality of pin members, and a plurality of slots. A gas filling implement makes it possible to fill the gas filling chamber with compressed gas in a simple and reliable manner without providing the gas spring with a gas filling valve having a nonreturn valve. Consequently, the entire gas spring is configured symmetrically about the axial center of the rod member, and its center of gravity is aligned with the axial center of the rod member, making it possible to prevent the gas spring from inducing vibrations in the main shaft.
The gas spring of the present invention comprises a cylindrical rod member with a piston, a cylinder main body fitted over the rod member, and an annular gas filling chamber filled with compressed gas and disposed between the rod member and the cylinder main body. This gas spring further comprises a first sealing member fitted over the piston portion of the rod member at one end of the gas filling chamber. A second sealing member is fitted into the cylinder main body at the other end of the gas filling chamber. A plurality of pin members are disposed in an axially symmetrical fashion about the rod member. A plurality of slots are provided to the cylinder main body to allow individual mating with the plurality of pin members and to restrict the range of movement of the rod member in relation to the cylinder main body. Thus, the cylinder main body is moved axially in relation to the rod member while the second sealing member is prevented from separating from the rod member in a state in which the pin members are not yet mounted. The gas filling chamber is filled with compressed gas through the slots. The cylinder main body is then moved back and the pin members are locked in place.
When the pin members are mounted, they mate with the slots formed in the cylinder main body, and the rod member is restricted in its ability to move relative to the cylinder main body. When the movement range is restricted in this manner, the gap between the rod member and the cylinder main body at the two ends of the gas filling chamber is sealed by the first and second sealing members, and the gas filling chamber is kept in an airtight state. Consequently, the pressure of the compressed gas in the gas filling chamber acts on the piston portion to create a situation in which the rod member is urged to move relative to the cylinder main body.
For example, the gas spring can be used as a drive mechanism for urging a drawbar on the main shaft of a machine tool toward a tool fastening side in order to fasten the tool on the main shaft. In this case, using a hollow rod member is preferred in order to allow the drawbar to be inserted into the rod member. It is apparent, however, that this concept can also be adapted to a variety of other devices or mechanisms required to perform drive functions.
The pin members are removed when the gas filling chamber is being filled with compressed gas. The pin members are disengaged without being mounted from the slots formed in the cylinder main body, thus removing restrictions on the range of movement of the rod member in relation to the cylinder main body. It is possible at this point to fill the gas filling chamber with compressed gas through the slots as the cylinder main body is axially moved relative to the rod member while the second sealing member is prevented from separating from the rod member (for example, in a state in which at least some of the slots are positioned on the external periphery near one end of the gas filling chamber). The cylinder main body is then returned to its original position, the gas filling chamber is rendered airtight, the compressed gas in the gas filling chamber is sealed, and the pin members are locked in place by being mated with individual slots, completing the introduction of the compressed gas.
Using the gas spring in accordance with the above-described routine allows the gas filling chamber to be filled with compressed gas in a simple and accurate manner. This makes it possible to dispense with the gas filling valve and allows the pin members, as well as the slots or other elements in engagement with these pin members, to be arranged symmetrically about the axial center of the rod members. It is therefore possible to configure the entire gas spring as a structure symmetrical about the axial center of the rod member and to align its center of gravity with the axial center of the rod member, allowing any reduction in machining accuracy to be securely prevented because the gas spring is prevented from creating vibration even when a main shaft rotates at a high speed in cases in which, for example, the gas spring is used as a drive mechanism for urging a drawbar on the main shaft of a machine tool toward the tool fastening side in order to fasten a tool to the main shaft.
According to a feature of the present invention, a gas spring comprises a cylindrical rod member with a piston, a cylinder main body fitted over the rod member, and an annular gas filling chamber filled with compressed gas and disposed between the rod member and the cylinder main body. This gas spring further comprises a first sealing member fitted over the rod member at one end of the gas filling chamber. A second sealing member is fitted into the cylinder main body at the other end of the gas filling chamber. A stopper member is fitted internally and threadably engaged with the cylinder main body and slidably fitted over the rod member on the opposite side from the gas filling chamber in relation to the piston portion of the rod member. Thus, the rod member is moved axially in relation to the cylinder main body while the first sealing member is prevented from reaching the threaded hole for the stopper member of the cylinder main body in a state in which the stopper member is not yet mounted. The gas filling chamber is then filled with compressed gas through a rod insertion hole facing the second sealing member. The rod member is then moved back, and the stopper member is mounted.
When mounted, the stopper member is slidably fitted over the rod member on the opposite side from the gas filling chamber in relation to the piston portion of the rod member. The stopper member is internally fitted and threadably engaged with the cylinder main body. The range of movement of the rod member in relation to the cylinder main body is thereby restricted by the stopper member. When the movement range is restricted in this manner, the gap between the rod member and the cylinder main body at the two ends of the gas filling chamber is sealed by the first and second sealing members, and the gas filling chamber is kept in an airtight state. Consequently, the pressure of the compressed gas in the gas filling chamber acts on the piston portion and creates a situation in which the rod member is urged to move relative to the cylinder main body.
The stopper member is removed when the gas filling chamber is being filled with compressed gas. When the stopper member is not mounted, there are no restrictions on the range of movement of the rod member in relation to the cylinder main body. It is possible at this point to fill the gas filling chamber with compressed gas through the rod insertion hole facing the second sealing member in a state in which the rod member is axially moved relative to the cylinder main body while the first sealing member is prevented from reaching the threaded hole for the stopper member of the cylinder main body (for example, in a state in which the rod member is removed from the rod insertion hole facing the second sealing member). The rod member is then returned to its original position, the gas filling chamber is rendered airtight, the compressed gas in the gas filling chamber is sealed, and the sealing member is then mounted, completing the introduction of the compressed gas.
Using the gas spring in accordance with the above-described routine allows the gas filling chamber to be filled with compressed gas in a simple and accurate manner. This makes it possible to dispense with the gas filling valve, to configure the entire gas spring as a structure symmetrical about the axial center of the rod member, and to align its center of gravity with the axial center of the rod member. Consequently, vibration sources are removed and any reduction in machining accuracy is securely prevented, even when the spring is mounted on the main shaft of a machine tool and the main shaft rotates at a high speed.
The present invention also provides a gas filling method for introducing compressed gas into a gas spring comprising a cylindrical rod member with a piston, a cylinder main body fitted over the rod member, an annular gas filling chamber filled with compressed gas and disposed between the rod member and the cylinder main body, a first sealing member fitted over the piston portion of the rod member at one end of the gas filling chamber, a second sealing member fitted into the cylinder main body at the other end of the gas filling chamber, a plurality of pin members disposed in an axially symmetrical fashion about the rod member, and a plurality of slots provided to the cylinder main body to allow individual mating with the plurality of pin members and to restrict the range of movement of the rod member in relation to the cylinder main body. This gas filling method is characterized in that the gas spring is placed in a special gas filling implement in a state in which the pin members are not yet mounted. The cylinder main body is moved axially in relation to the rod member while the second sealing member is prevented from separating from the rod member. The gas filling chamber is filled with compressed gas through the gas filling implement and the slots. The cylinder main body is then moved back, and the pin members are locked in place.
When the gas filling chamber is to be filled with compressed gas, the gas spring is placed in a gas filling implement, and the pin members are removed. The pin members are disengaged without being mounted from the slots formed in the cylinder main body, thus removing restrictions on the range of movement of the rod member in relation to the cylinder main body. In this state, the cylinder main body is moved axially in relation to the rod member, while the second sealing member is prevented from separating from the rod member. The gas filling chamber is filled with compressed gas through the gas filling implement and the slots.
The cylinder main body is then returned to its original position, the gas filling chamber is rendered airtight, the compressed gas in the gas filling chamber is sealed, the pin members are locked in place, and the gas spring is removed from the gas filling implement, completing the introduction of the compressed gas. Specifically, filling the gas spring with gas in the this manner allows the gas filling chamber to be filled with compressed gas in a simple and accurate manner without the use of a gas filling valve. It is therefore possible to configure the entire gas spring as a structure symmetrical about the axial center of the rod member and to align its center of gravity with the axial center of the rod member when the gas spring is filled with compressed gas in accordance with the proposed gas filling method. A gas filling valve equipped with a nonreturn valve can be mounted on the gas filling implement, and the gas filling chamber can be filled with compressed gas through the gas filling valve.
The special gas filling implement has an inner cylinder airtightly fittable over the slot-free portion of the cylinder main body, an outer cylinder configured to extend all the way to one end the inner cylinder and to slidably fit over the inner cylinder in an airtight fashion, a blocking member configured to block one end of the rod member and to airtightly fit into the end portion of the outer cylinder, an axial hole blocking member airtightly inserted into the axial hole of the rod member on the opposite side from the blocking member, and a compressed gas filling conduit formed in the axial hole blocking member.
When the gas filling chamber is to be filled with compressed gas, the gas spring is placed in the gas filling implement, and the area defined by the inner cylinder, outer cylinder, and blocking member outside the rod member is made into a sealed space. The cylinder main body is moved axially in relation to the rod member while the second sealing member is prevented from separating from the rod member in a state in which the pin members are not mounted, allowing the compressed gas introduced into the sealed space through the axial hole of the rod member to be further guided into the gas filling chamber through the slots in a reliable manner. The threaded hole for the pin member formed in the rod member can be used as a gas conduit that leads from the axial hole of the rod member to the sealed space.
The present invention provides another gas filling method for introducing compressed gas into a gas spring comprising a cylindrical rod member with a piston, a cylinder main body fitted over the rod member, an annular gas filling chamber filled with compressed gas and disposed between the rod member and the cylinder main body, a first sealing member fitted over the rod member at one end of the gas filling chamber, a second sealing member fitted into the cylinder main body at the other end of the gas filling chamber, and a stopper member internally fitted and threadably engaged with the cylinder main body and slidably fitted over the rod member on the opposite side from the gas filling chamber in relation to the piston portion of the rod member. This gas filling method for a gas spring is characterized in that the gas spring is placed in a special gas filling implement in a state in which the stopper member is not yet mounted. The rod member is moved axially in relation to the cylinder main body while the first sealing member is prevented from reaching the threaded hole for the stopper member of the cylinder main body. The gas filling chamber is filled with compressed gas through the gas filling implement and a rod insertion hole facing the second sealing member. The rod member is then moved back, and the stopper member is mounted.
When the gas filling chamber is to be filled with compressed gas, the gas spring is placed in a gas filling implement, and the stopper member is removed. When the stopper member is not mounted, the rod member is not restricted in terms of the range within which the member can move in relation to the cylinder main body. The rod member is moved axially in relation to the cylinder main body while the first sealing member is prevented from reaching the threaded hole for the stopper member of the cylinder main body in this state, and the gas filling chamber is filled with compressed gas through the gas filling implement and a rod insertion hole facing the second sealing member.
The rod member is then returned to its original position, the gas filling chamber is rendered airtight, the compressed gas in the gas filling chamber is sealed, the stopper member is mounted, and the gas spring is removed from the gas filling implement, completing the introduction of the compressed gas. Specifically, filling the gas spring with gas in accordance with this method allows the gas filling chamber to be filled with compressed gas in a simple and accurate manner without the use of a gas filling valve. It is therefore possible to configure the entire gas spring as a structure symmetrical about the axial center of the rod member and to align its center of gravity with the axial center of the rod member when the gas spring is filled with compressed gas in accordance with the proposed gas filling method. A gas filling valve equipped with a nonreturn valve can be mounted on the gas filling implement, and the gas filling chamber can be filled with compressed gas through the gas filling valve.
The special gas filling implement includes a casing member, having an opening on one side of the stopper member and possessing a housing chamber in which the gas spring can be airtightly accommodated while the rod member is moved axially in relation to the cylinder main body; a blocking member, fitted into the opening in an airtight and slidable manner, designed to be able to come into contact with the rod member; a pull rod, inserted into the axial center of the gas spring, designed such that one end thereof is immovably mounted on the blocking member, and the other end thereof is airtightly inserted into the casing member; and a gas filling conduit, formed in the casing member, used to fill the housing chamber with compressed gas.
The housing chamber containing the gas spring is rendered airtight in a state in which the gas spring is placed in the gas filling implement. It is possible to adopt an arrangement in which the rod member moves axially in relation to the cylinder main body by the pull rod while the first sealing member is prevented from reaching the threaded hole for the stopper member of the cylinder main body. The gas filling chamber is filled with compressed gas, and the rod member is accurately returned to its original position together with the blocking member by the pulling of the pull rod following the introduction of compressed gas.